This invention relates to a bi-directional sealing assembly having application in valves, especially butterfly valves. Butterfly valves have many advantages over other type valves in fluid flow regulation, most notable of these being low cost of manufacture, quickness of opening and low restriction to fluid flow when fully open. However, these valves have generally been limited to low pressure applications because of their inability to seal tightly at high pressures. In some prior art valves, the seals are located in grooves. In high pressure applications these seals often become dislodged from the grooves when the valves are opened, thereby rendering the valves inoperative. In others, elaborate groove arrangements for preventing seal blow-out increase the initial cost of the valve, raise the cost for repair or replacement of the seals, and increase the possibility of seal damage and misalignment. In several types of valves, the contact between the disc and valve must be made so tight to prevent leakage, that opening the valve, especially large size valves, requires a large torque. In some prior art valves utilizing a groove and an elastomeric seal, the seal can cold flow under the sealing pressures experienced, thereby decreasing seal life.
In several of these prior art valves, the seat ring has a "V" shaped groove in the rear surface in which is located a back-up ring. Both rings are located in a "T" shaped slot in the valve body. Upstream fluid under pressure enters the slot and moves the back-up ring along the groove to thereby force the seat ring forward into tighter engagement with the disc. This type of seal assembly has several inherent disadvantages which are overcome by the seal assembly of this application. Machining the inner surfaces of the "T" shaped slot is difficult. An inadequate finish on these surfaces will cause excessive wear on the seat ring and back-up ring operating in the slot resulting in early seal failure. Furthermore, the downstream section of the seat ring may deflect under the fluid pressure, resulting in possible back-up ring extrusion and damage. In addition, installation of the back-up ring and seat ring into the slot is usually difficult, requiring special techniques and frequently causing seal misalignment. Furthermore, these seals usually are not bi-directional, sealing better when the upstream side of the seal is on a particular side of the valve stem.
An object of the present invention is to provide an improved valve seal assembly which will seal tightly at high pressures, will not blow out under high system pressures, and which is operable with a relatively low torque.
A further object is to provide a relatively inexpensive, long-wearing, easily replaceable valve seal assembly.
A still further object is to provide a valve seal assembly which effectively prevents fluid flow in either direction at high pressure when the valve is closed.
The seat ring which is the subject of this invention comprises a novel combination of seat ring and recess design. In preferred embodiments of the invention shown and discussed herein, a back-up means may also be added to improve the seal performance, although the back-up means is not essential to the successful practice of every embodiment of this invention. The seat ring is located in a recess having an inverted "V" shaped section, the walls of which are easily accessible for providing a smooth finish for an extended seal life. The back-up means, if utilized, is located in the recess communicating with the seat ring. In each of the embodiments shown, fluid is permitted to enter the upstream side of the recess where it operates on the seat ring and back-up ring combination to effect fluid-tight seals with both the downstream side of the recess and with the valve closure means.